What does Acts 8:15 mean?

This and the following verses are among those passages of Scripture which require careful understanding of context and clear explanation. Philip, a Hellenistic Jewish Jesus-follower, has been evangelizing in a city of mixed-Jewish Samaritans. Many of these Samaritans are ready to follow Jesus. They've even been baptized. But they haven't yet received the Holy Spirit. John and Peter have come from Jerusalem to pray over the new converts and lay their hands on them so they can receive the Holy Spirit (Acts 8:9–14).

It's important to understand that this is a description of events used by God to establish the very early church as it spread to people outside the devout Jewish community. The Holy Spirit waiting for Peter and John is no more the norm than the Holy Spirit waiting for the Day of Pentecost and imbuing the initial Jesus-followers with tongues of fire (Acts 2:1–4). Peter and John don't come because the Holy Spirit needs them, but because God wants to validate the new Samaritan church in two ways.

First, although Philip is known as a strong Jesus-follower and one of the first deacons (Acts 6:1–6), and although his message has been validated by miraculous signs (Acts 8:6–7), it's important for the Samaritans to have absolute certainty that they are joining the established church that worships Jesus of Nazareth as the Messiah and their way of salvation. Philip is a great man, but he's a deacon, not an elder of the church in Jerusalem, as the apostles are. Peter and John are known to be the foremost of Jesus' original followers. Their validation of Philip's message is somewhat similar to Jesus' validation of John's baptism (Matthew 3:13–17).

Second, the church in Jerusalem needs to validate that the Holy Spirit really can come to Samaritans. Samaritans haven't properly worshiped God since Jeroboam built two gold calves in order to keep his new kingdom religiously and politically separated from their kin in the southern kingdom (1 Kings 12:25–33). This validation is especially important for Peter, as he continues to have trouble understanding how people who are not Jewish can be accepted into what he sees as the ultimate fulfillment of Judaism (see Acts 10 and Galatians 2:11–14).